Force-applying tools

ABSTRACT

Force-applying hand tools, such as wrench sockets, are disclosed produced by powder metallurgy. The working portion of the tool comprises a porous sintered body of heat treatable steel composition of high strength having an average density of at least 85 percent of true density and having an adherent plating of a protective metal coating on the surface thereof.

United States Patent Talmage [4 1 June 13, 1972 [54] FORCE-APPLYIN GTOOLS [56] References Cited UNITED STATES PATENTS 2,491,839 12/1949Tinkler ..204/29 2,897,097 7/1959 Smith et a1. ..117/50 X 3,506,3834/1970 Ewalt ...29/182.3 X

2,489,839 11/1949 Whitney 148/165 2,826,805 3/1958 Probst et al .148/126X 2,827,407 3/1958 Carlson et al.... ..29/182 3,360,347 12/1967 Todd..75/222 OTHER PUBLICATIONS Precision Metal Molding, Jan. 1953, pp. 47-49 Metal Finishing, Nov. 1955, pp. 70- 73 Primary Examiner-Charles N.Lovell Attorney-Robert S. Smith, David S. Urey, Alan C. Rose and AlfredB. Levine 5 7] ABSTRACT Force-applying hand tools, such as wrenchsockets, are disclosed produced by powder metallurgy. The workingportion of the tool comprises a porous sintered body of heat treatablesteel composition of high strength having an average density of at least85 percent of true density and having an adherent plating of aprotective metal coating on the surface thereof.

10 Claims, 7 Drawing Figures FORCE-APPLYING TOOLS This is a division ofapplication Ser. No. 637,391, filed May 10, 1967, now U.S. Pat. No.3,506,500 issued Apr. 14, 1970.

The invention relates to force-applying tools, such as socket wrenches,pliers, parts for ratchet wrenches, and the like, and to a powdermetallurgy method for producing such tools.

In the production of certain hand tools, such as wrench sockets, pliersand similar tools, generally steel bar stock is employed from which thetools are fabricated using conventional forming methods, such as dropforging and machining methods. For example, in producing a wrenchsocket, cylindrical'bar stock is often employed which is machined intothe desired configuration utilizing, for example, an automatic screwmachine. The amount of machining required generally results in about 60to 65 percent of the metal being recovered in the final product, theremainder being lost as machining scrap.

Certain hand tools, such as pliers, are produced by drop forging. Theamount of recovered metal in the final product ranges from about 60 to70 percent, the remainder being lost as flash material and due tocropping away of excess metal upon completion of the forging operation.

The steel bar stock employed in producing the foregoing type of tools isgenerally produced by hot rolling. Such bar stock usually hasdirectional properties; that is to say, the physical properties in thelongitudinal direction are generally higher than in the transversedirection. Thus, depending on the method of manufacture, the cleanlinessof the metal, etc., such steels may not always have the desiredtransverse properties to meet specification requirements. Wrenchsockets, for example, are usually subjected to high torque stresses inuse and it is desirable that the steel from which the wrench is madehave generally high but uniform physical properties in both thetransverse and longitudinal directions.

It is an object of the invention to provide as an article of manufactureforce-applying hand tools produced by powder metallurgy.

Another object is to provide a powder metallurgy method for producingforce-applying tools characterized by an improved combination ofphysical properties.

A still further object is to provide a more economical and efficientmethod for producing hand tools.

These and other objects will more clearly appear when considered in thelight of the following disclosure and the accompanying drawing, wherein:

FIGS. 1 to 3 are illustrative of a hexagonal wrench socket produced inaccordance with the invention;

FIGS. 4 and 5 depict in plan and elevation a plier element; and

FIGS. 6 and 7 are reproductions of photomicrographs comparing themetallographic structure of a steel composition produced conventionallywith one produced by power metallur S thting it broadly, the inventionprovides as an article of manufacture a force-applying tool comprising aporous sintered body of a heat treatable steel composition having adensity less than true density, but which density at or near the surfaceof said sintered body is at least 89 percent of true density, theaverage density of the sintered body being at least 85 percent, and,more advantageously, at least 89 percent.

An advantageous feature of the tool comprising said sintered body isthat, despite its porosity, it meets specification strengthrequirements, is generally much cleaner than steels made by theconventional methods of melting, casting and hot working, is generallyfree of directional properties, and moreover is more economical toproduce. For example, in producing such tools utilizing powdermetallurgy techniques, the metal yield in the final product is generallyat least about 98 percent by weight of the starting material as comparedto convention methods of production where a metal yield of about 65percent is often considered normal. In addition, by controlling themetallurgical structure of the final product, an average density ofabout 85 to 97 percent can be utilized without substantially sacrificingthe strength properties of the tool, while at the same time achieve asaving in raw material costs due to weight reduction and greatly reducedscrap loss.

In carrying the invention into practice, iron powder of highcompressibility is employed to which a steel-forming ingredient isadded, such as carbon with or without alloying additions, for example,nickel. Where the steel employed is plain carbon steel, the amount ofcarbon may range from about 0.3 to 0.8 percent, with the balanceessentially iron. Where a nickel steel is employed, the composition maycomprise about 1 to 5 percent nickel, about 0.3 to 0.8 percent carbonand the balance substantially iron. More advantageously the compositionmay contain about 1.5 to 3.5 percent nickel, about 0.3 to 0.6 percentcarbon and the balance essentially iron. Steels which may be employedmay include, low, medium and high alloy steels, just so long as thesteels are heat treatable, that is capable of being heat treated to forman austenitic decomposition product, such as pearlite annealed),martensite (hardened) or other austenitic decomposition products. Theterms balance essentially or balance substantially" iron are meant toinclude the presence of other elements normally employed in steelcompositions.

A metallurgical structure found particularly advantageous for thepurposes of the invention is one in which the sintered tool element hasa density varying from about to 97 percent of true density in thehardened condition, and in addition has a hardened surface zone ofhigher density produced by gas carburizing or by carbo-nitriding, itbeing understood that the term carburized covers the foregoing methodsof surface hardening. The hardened surface advantageously has anadhering metal plating comprising a metal selected from the groupconsisting of Cu, Zn, Cd, Ni and Cr. The hardened surface zone of higherdensity is important in that it reinforces the hardened porous substrateand makes it resistant to brinelling, that is, resistant to knicking andthe like, the metal plate conferring resistance to corrosion to thetool. The hardened surface of higher density is further advantageous inthat it insures metal plating of high quality.

As illustrative of the invention, the following example is given:

In producing a hexagonal wrench socket of the type shown in FIGS. 1 to3, atomized iron powder of high compressibility and average particlesize of about approximately 75 microns is employed having an ironcontent of at least about 98 percent, with the balance small amounts ofother ingredients, such as manganese, silicon, etc. To the iron is added2 percent weight of carbonyl nickel powder of about 99.9 percent purityand of average particle size ranging from about 3 to 5 microns, andsufi'rcient carbon as natural graphite (about 5 microns average size) toprovide a final carbon content of about 0.3 percent. About 1 percent byweight of lithium stearate is added and the mix blended by conventionalmeans for about 1 hour.

Upon completion of the mixing, a given volume of the blended powder ispressed in a double acting die having a configuration corresponding tothe wrench socket of FIGS. 1 to 3. The pressure generally ranges fromabout 30 tons per square inch to l 10 tons per square inch. In producingwrench socket having an CD. of about 0.4375 inch, a total pressure ofabout 10 tons was employed which corresponded to a pressure of almost108 tons per square inch, the green density after pressing beingapproximately 91 percent.

After pressing, the tool element is then subjected to sintering in anatmosphere of cracked ammonia at a temperature of about 2,020 to 2,080F. for about 10 to 40 minutes, the density after sintering remainingsubstantially unchanged. The apparent hardness as sintered ranges fromabout 50 to 60 R The tool element is thereafter subjected to heattreatment by heating it to an austenitizing temperature of about 1,650F. and holding it at temperature for from 10 to 15 minutes in anatmosphere of cracked ammonia containing about 1 percent by volume ofpropane, the propane being using to avoid decarburization and to providea thin carburized higher density case to the porous surface of the tool.The tool is then quenched from this temperature into a bath of fastquenching oil to convert the microstructure to martensite, with theapparent hardness ranging from about 45 to 55 Rc. After the tool hasbeen hardened, it is then drawn at 450 F. for about 1 hour to lower theapparent hardness to about 38 to 43 Re.

The tool is then provided with a metal plating comprising a metalselected from the group consisting of Cu, Zn, Cd, Ni and Cr by usingconventional metal plating techniques, such as barrel or rack plating.

As will be appreciated, in carrying out the sintering and platingtreatments, a plurality of tool elements would be handied at one time.Likewise, in producing the various tool parts, an automatically operablepress may be employed. In sintering the parts, this may be donecontinuously by utilizing an endless conveyor passing through thesintering furnace.

In producing wrench sockets of the type shown in FIG. 1, it is desirablethat the corners of the hex 10 have a radius of curvature 11 to avoidhigh stress concentration at the comers during use.

Referring to FIG. 3, a cross section of the socket wrench is shownhaving a porous substrate 12 and a metal coating 13. FIGS. 4 and 5 areillustrative of another force applying tool showing in plan andelevation one-half of a pair of pliers 14 produced in a similar manneras the socket wrench of FIGS. 1 to 3.

As has been stated hereinbefore, one of the advantages of the inventionis that it enables the production of tools having uniform properties inboth the transverse and longitudinal direction as compared toconventionally produced tools. In addition, the metallographic structureof the tool produced by the invention is generally cleaner. Asillustrative of the foregoing, reference is made to FIGS. 6 and 7 whichdepict the metallographic structure of a conventionally produced tool(FIG. 6) and the tool produced by the invention (FIG. 7).

Referring to FIG. 6, which is a representation of a micrograph of ascrew machine blank taken at 2OOX diameter, elongated non-metallicinclusions are shown running in a longitudinal direction. Generally,such structures have directional longitudinal properties at thesacrifice of transverse properties. Such direction properties in awrench socket results in reduced torque strength.

On the other hand, FIG. 7, which is a representation of a micrograph ofa sintered blank taken at 200X diameter, shows no elongated inclusion inthe substantially uniform structure. It will be noted from FIG. 7 thatthere is a thin densified zone below the metal plate.

Broadly speaking, the method aspect of the invention comprises 1)providing a batch of metal powder comprising a heat treatable steelcomposition containing about 0.3 to 0.8 percent carbon; (2) confining ameasured quantity of the powder into a cavity of a die having a finalconfiguration of the hand tool element desired; (3) pressing theconfined powder at a pressure ranging from about 30 to 110 tsi; thepressure being selected to provide a pressed density of at least 85percent of true density; (4) sintering the element at an elevatedtemperature e.g. about 1,800 to 2.200 F. or more, advantageously fromabout 2,0l to 2,080 F., in a protective atmosphere that does notadversely affect the carbon content of the steel for a time sufficientto produce a high strength product; (5) heat treating the sinteredproduct by heating it to an austenitizing temperature in an atmosphereprotective to the carbon content of the steel, preferably an atmosphereprotective to the carbon content of the steel, preferably an atmospherecontaining a small amount of carburizing gas; (6) quenching the productat a rate to form martensite followed by tempering; and (7) then platingthe surface of the heat treated porous tool body with a protective metalcoating, such as a metal coating selected from the group consisting ofCu, Zn, Cd, Ni and Cr.

Microscopic examination of etched samples of sintered nickel steelsockets produced in accordance with the invention reveals a generallyheterogeneous structure characterized by a dispersion throughout thesteel matrix of a plurality of bright nickel-rich areas. Tests haveindicated that sintered tools having such nickel alloy structuresexhibit good mechanical properties.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the invention and the appended claims.

What is claimed is:

1. As an article of manufacture a force-applying hand tool having aworking portion with which force is applied during use, said portioncomprising a porous sintered body of a heat treatable steel compositioncontaining about 0.3 to 0.8 percent carbon and the balance essentiallyiron having a density at and near the surface of said portion of atleast 89 percent of true density, and a smooth adherent plating of metalselected from the group consisting of Cu, Zn, Cd, Ni and Cr covering thesurface of said porous sintered body and the metallographic structure ofthe porous sintered body is characterized by an austenitic decompositionproduct, wherein the surface of said porous sintered body has acarburized zone and wherein said metal plating covers and adheres tosaid carburized zone.

2. The hand tool of claim 1, wherein said body portion is a wrenchsocket.

3. As an article of manufacture a force-applying hand tool having aworking portion with which force is applied during use, said portioncomprising a porous sintered body of a heat treatable steel compositioncontaining about 1 to 5 percent nickel, about 0.3 to 0.8 percent carbonand the balance essentially iron and having a density at and near thesurface of said portion of at least 89 percent of true density, and asmooth adherent plating of metal selected from the group consisting ofCu, Zn, Cd, Ni and Cr covering the surface of said porous sintered body.

4. The hand tool of claim 5, wherein the nickel in the sintered steelcomposition is substantially dispersed throughout the steel matrix asnickel rich areas.

5. As an article of manufacture a force-applying hand tool having aworking portion with which force is applied during use, said portioncomprising a porous sintered body of a heat treatable steel compositioncontaining about 1.5 to 3.5 percent nickel, about 0.3 to 0.6 percentcarbon and the balance essentially iron and having a density at and nearthe surface of said portion of at least 89 percent of true density, anda smooth adherent plating of metal selected from the group consisting ofCu, Zn, Cd, Ni and Cr covering the surface of said porous sintered bodyand said body portion is a wrench socket.

6. As an article of manufacture a force-applying hand tool having aworking portion with which force is applied during use, said portioncomprising a porous sintered body of a heat treatable steel compositioncontaining about 0.3 to 0.8 percent carbon and the balance essentiallyiron wherein the average density of said porous sintered steel bodyranges from about 89 to 97 percent of true density and a smooth adherentplating of metal selected from the group consisting of Cu, Zn, Cd, Niand Cr covering the surface of said porous sintered body.

7. As an article of manufacture a force-applying hand tool having aworking portion with which force is applied during use, said portioncomprising a porous sintered body of a heat treatable steel compositioncontaining about 0.3 percent to 0.8 percent carbon and the balanceessentially iron having an average density less than true density butbeing at least percent of true density, the density at and near thesurface of said portion being greater than the average density and atleast 89 percent of true density, and a smooth adherent plating of metalselected from the group consisting of Cu, Zn, Cd, Ni and Cr covering thesurface of said porous sintered body and the metallographic structure ofthe porous sintered body is characterized by an austenitic decompositionproduct,

but being at least percent of true density, the density at and near thesurface of said portion being greater than the average density and atleast 89 percent of true density, and a smooth adherent plating of metalselected from the group consisting of Cu, Zn, Cd, Ni and Cr covering thesurface of said porous sintered body.

10. The hand tool of claim 9, wherein the nickel in the sintered steelcomposition is substantially dispersed throughout the steel matrix asnickel rich areas.

2. The hand tool of claim 1, wherein said body portion is a wrenchsocket.
 3. As an articlE of manufacture a force-applying hand toolhaving a working portion with which force is applied during use, saidportion comprising a porous sintered body of a heat treatable steelcomposition containing about 1 to 5 percent nickel, about 0.3 to 0.8percent carbon and the balance essentially iron and having a density atand near the surface of said portion of at least 89 percent of truedensity, and a smooth adherent plating of metal selected from the groupconsisting of Cu, Zn, Cd, Ni and Cr covering the surface of said poroussintered body.
 4. The hand tool of claim 5, wherein the nickel in thesintered steel composition is substantially dispersed throughout thesteel matrix as nickel rich areas.
 5. As an article of manufacture aforce-applying hand tool having a working portion with which force isapplied during use, said portion comprising a porous sintered body of aheat treatable steel composition containing about 1.5 to 3.5 percentnickel, about 0.3 to 0.6 percent carbon and the balance essentially ironand having a density at and near the surface of said portion of at least89 percent of true density, and a smooth adherent plating of metalselected from the group consisting of Cu, Zn, Cd, Ni and Cr covering thesurface of said porous sintered body and said body portion is a wrenchsocket.
 6. As an article of manufacture a force-applying hand toolhaving a working portion with which force is applied during use, saidportion comprising a porous sintered body of a heat treatable steelcomposition containing about 0.3 to 0.8 percent carbon and the balanceessentially iron wherein the average density of said porous sinteredsteel body ranges from about 89 to 97 percent of true density and asmooth adherent plating of metal selected from the group consisting ofCu, Zn, Cd, Ni and Cr covering the surface of said porous sintered body.7. As an article of manufacture a force-applying hand tool having aworking portion with which force is applied during use, said portioncomprising a porous sintered body of a heat treatable steel compositioncontaining about 0.3 percent to 0.8 percent carbon and the balanceessentially iron having an average density less than true density butbeing at least 85 percent of true density, the density at and near thesurface of said portion being greater than the average density and atleast 89 percent of true density, and a smooth adherent plating of metalselected from the group consisting of Cu, Zn, Cd, Ni and Cr covering thesurface of said porous sintered body and the metallographic structure ofthe porous sintered body is characterized by an austenitic decompositionproduct, wherein the surface of said body has a carburized zone andwherein said metal plating covers and adheres to said carburized zone.8. The hand tool of claim 7, wherein said body portion is a wrenchsocket.
 9. As an article of manufacture a force-applying hand toolhaving a working portion with which force is applied during use, saidportion comprising a porous sintered body of a heat treatable steelcomposition comprising about 1 to 5 percent nickel, about 0.3 to 0.8percent carbon, and the balance essentially iron having an averagedensity less than true density but being at least 85 percent of truedensity, the density at and near the surface of said portion beinggreater than the average density and at least 89 percent of truedensity, and a smooth adherent plating of metal selected from the groupconsisting of Cu, Zn, Cd, Ni and Cr covering the surface of said poroussintered body.
 10. The hand tool of claim 9, wherein the nickel in thesintered steel composition is substantially dispersed throughout thesteel matrix as nickel rich areas.